Step 1Bring the water to a boil and cook the onion and zucchini until the squash is tender-crisp, 12 to 15 minutes. Remove from the heat and drain.
Step 2Heat the oven to 375 degrees. Grease a 1 1/2-quart casserole.
Step 3Combine the zucchini, onion, cheese, beaten eggs, salt, pepper, chiles and tomatoes in a mixing bowl, then pour into the casserole. Top with the corn bread stuffing mix and dot with butter.
Step 4Bake until the corn bread stuffing is golden brown, 40 minutes. Place the casserole under the broiler briefly to brown the top, 2 to 3 minutes.