"This French dish uses loads of Mediterranean vegetables and is a perfect way to use up the zucchini flooding your garden! We like to add chicken to ours to make it a whole meal, and we usually serve it over rice. We usually do half a breast per person. This is our family's version, so it doesn't have the eggplant or the fresh tomatoes that you see in most traditional ratatouille recipes (maybe when the kids grow up a little?), but this recipe did get the kids to start eating zucchini and mushrooms, which we never thought would happen!"
Heat olive oil in a skillet over medium-high heat. Add chicken and onion; saute until chicken is still slightly pink in the center, 3 to 5 minutes. Add yellow squash, green zucchini, red bell pepper, and mushrooms. Cook and stir until slightly softened, about 4 minutes. Add garlic; cook, stirring frequently, until fragrant, about 3 minutes more.
Pour chicken stock into skillet and add tomato paste. Stir in herbes de Provence, cumin, oregano, and celery salt. Stir well. Continue to cook and stir, adding more liquid if necessary, until vegetables are cooked to your preference, 4 to 8 minutes more. Season with salt and pepper.
If you don't have herbes de Provence, you can substitute 1 tablespoon Italian seasoning or 2 to 3 tablespoons of fresh herbs on hand (parsley and/or rosemary and basil are good). If you don't have celery salt, you can use seasoning salt.
You can mince the red onion if you have picky eaters who would be suspicious of the strips.
After adding garlic, you could also add 2 cups cubed eggplant and/or two diced tomatoes.
You can use water in place of chicken stock if desired.