Spray a large nonstick skillet over medium-high. Add mushrooms, bell pepper, and zucchini, and sauté until vegetables soften slightly, about 3 minutes. Add marinara and simmer to heat through. Reduce heat to low and keep warm.
Bring milk and salt to a boil in a medium saucepan over medium-high. Slowly whisk in polenta, stirring constantly to prevent lumps from forming. Cook until thickened, about 5 minutes. Remove from heat, cover, and keep warm.
Heat 2 teaspoons oil in a large nonstick skillet over medium-high. Carefully crack eggs into pan and cook until whites are set and yolks are cooked to desired doneness, 4 to 6 minutes.
To serve, divide polenta among 4 shallow serving bowls; top with marinara and an egg. Sprinkle with chopped basil if desired.
Nutrition figures based on using fat free milk.