Slice the andouille sausage into thin coins on the bias.
Add the olive oil to a large nonstick pan over medium heat. Add the sausage and onion and saute until the sausage is seared and browned. Add the garlic, peppers, squash and zucchini, season with salt and pepper and lightly saute about 2 minutes (you still want the zucchini and squash to have a bite and be very al dente). Add the rice to the pan with the sausage and veggies, stirring to coat the rice with all of the flavors. Add the stock and saffron. Bring to a simmer, cover and cook until the rice is done, 10 to 15 minutes. Fold in the diced tomatoes and parsley.