Heat a heavy, oven safe large skillet over medium high heat, add a drizzle of olive to coat the bottom of the pan. Add the zucchini, yellow squash, and onion.
Add another drizzle of olive oil, followed by the chicken. Season chicken with a sprinkle of salt. Saute chicken, flipping occasionally, until golden brown on all sides and almost cooked through, about 5-8 minutes.
Reduce heat to medium, add a drizzle of olive oil if needed, followed by the garlic. Saute until garlic is translucent, about 1 minute. Add in the canned tomatoes, Italian seasoning, pesto, and a generous pinch of salt and pepper.
Using the back of a spoon or a potato masher, start breaking up the tomatoes until they integrate into the sauce. Simmer sauce for 15 to 20 minutes until reduced and thickened.