Place polenta slices on a baking sheet coated with cooking spray. Broil 3 1/2 inches from heat 5 minutes on each side or until lightly browned.
While polenta bakes, coat a large nonstick skillet with cooking spray; place skillet over medium-high heat until hot. Add pesto and water, stirring well. Add yellow squash and zucchini; cover and cook 5 minutes or until vegetables are tender. Add red peppers; cook until thoroughly heated.
To serve, spoon zucchini mixture evenly over polenta, and sprinkle with cheese.