Heat a non-stick skillet with oil over medium-high heat. When very hot, place fish filets skin side down and press down with the back of a spatula to flatten the filet and the skin is flush with the skillet (it tries to curl). Cook fish, pressing occasionally with the spatula, until the fish is nearly opaque and cooked through, with just a small raw area on the very top, about 6 minutes. Using a sturdy spatula, carefully flip the snapper and continue cooking until the top is cooked through and golden brown, about 3 more minutes. Remove fish from pan and let rest on a wire rack for 2-3 minutes, while the you prepare the zucchini and squash.