½ cup shredded Cheddar cheese
Preheat the oven to 350°F. Lightly oil a 9-inch pie plate with cooking spray.
Put the crust ingredients into a small bowl; mix thoroughly with a fork. Use the back of a spoon to press the mixture into the bottom and sides of the prepared pie plate; set aside.
Heat 1 tablespoon of the oil in a large skillet over medium-high heat. Add the bell peppers, celery, onion, and garlic. Cook, stirring occasionally, until the vegetables are crisp-tender, about 5 minutes. Remove from the heat. Stir in the remaining ingredients, except the cheeses. Taste and adjust the seasoning. Set aside.
Toss the two cheeses in a small bowl. Sprinkle about 1/3 of the cheese mixture over the crust; pour in the pie filling and spread evenly.
Bake for 30 minutes or until a knife inserted in the center comes out nearly clean. Sprinkle with the remaining cheese mixture; bake until the cheese is melted, about 10 minutes. Allow to stand for about 5 minutes before cutting into wedges for serving.
The crust and filling can be made up to 1 day in advance. Press the crust into the pan; cover and refrigerate. Refrigerate the filling in a separate covered container. Bring the crust and filling to room temperature; assemble and bake the pie just before serving.