Nine-year-olds Cheyenne Calkins, left, Catlynn Webster and Claire Wilson clear the way as group leader Sadie Keller teases them with an avocado peel Thursday at the Boys & Girls Club of Lawrence campus at East Heights. The kids spent the morning preparing culinary masterpieces to be judged in Top

After mixing up the avocados, onions, tomatoes and cilantro, the group of third-graders at the Boys & Girls Club of Lawrence had to name their guacamole. Suddenly it came to them.

“Whackamole,” proclaimed Kolton Scott, 9. “Because it whacks your taste buds!”

Stephen Ritz would agree with that description. On Thursday, the Boys & Girls Club invited Ritz, an urban-farming advocate who teaches at-risk kids in New York’s South Bronx, to Lawrence, where he toured several local sustainability projects before giving a speech at the Carnegie Building. But shortly after arriving, he got to judge a cooking competition, “Top Chef”-style, at the Boys & Girls Club’s East Heights campus.

Good thing he was hungry. The third-graders spent nearly an hour preparing their Mexican dishes, chopping vegetables, mashing guacamole and grilling quesadillas, to see who could impress Ritz the most. They took the task seriously. “That’s too much pepper,” Claire Wilson, 9, told one of her team members. “Too much pepper will ruin it!”

Using 9-year-old Kolton Scott as a prop, special guest Stephen Ritz tells kids from the Boys & Girls Club of Lawrence on Thursday that the amount of weight he has lost in recent months, 110 pounds, is nearly equivalent to the full weight of Kolton.

Ritz, through his Green Bronx Machine organization, has helped transform one of the densest and poorest parts of New York City, inspiring students and members of the community to plant urban gardens, whether on roofs, walls or medians. His disciples have to date grown more than 30,000 pounds of fresh produce.

“Do you know what my favorite expression is? ‘Sí se puede,'” he said, playing into the class’ Mexican theme. “Do you know what ‘Sí se puede’ means? ‘Yes we can.’ Because I believe that we all can, because we are all ‘Amer-I-cans.'”

Melanie Meyer and Charlotte Richardson showed Ritz some of the vegetables they have been growing in a garden in back of the school. He told them that using a black tarp would help with weed control.

The kids have already had success in the garden this year, harvesting peppers, potatoes, cucumbers and zucchini. The types of ideas Ritz espouses have already been getting through to the girls, who mentioned some of the benefits of the school garden.

“It’s fun because students can experience it firsthand,” said Meyer, 11.

“When you don’t have to go to the store, you don’t have to spend as much money,” added Richardson, 10.

After trying the “whackamole,” Ritz encouraged the group members to make more of their product, put it into jars, brand it and sell it. “Not only can you be green, you can make green,” said Ritz, who has inspired several of his students to become successful landscapers and farmers’ market vendors.

He also sprinkled in tips about healthy eating. He said that freshly made salsa is a nutritious substitute for ketchup, and that onions and tomatoes are good to eat because they make you feel full. Changing his diet has helped Ritz lose 110 pounds in recent months.

“I used to get a lot of the food off the 99-cent menu,” Ritz said. “Do you know why that’s bad?”

“That’s cheaper — that means it has a lot of calories,” answered Cade Crady, 9, impressing Ritz with his knowledge.

In the end, Ritz couldn’t pick just one champion.

“We’re all winners today, because if you eat healthy, you live healthy,” he said, his baggy clothes exemplifying exactly what he meant.