Bring 3 cups water to a boil in a medium saucepan. Add shrimp; cook 3 to 5 minutes or until shrimp turn pink. Drain and rinse under cold water.
While shrimp cook, chop onion, squash, and pepper; place in a large bowl. Add cooked shrimp, tomatoes, herbs, and picante sauce to vegetable mixture, stirring well. Cover and chill at least 10 minutes.