Preheat the oven to 325°F.2.
Heat olive oil in a large skillet over medium heat.
When hot, add garlic and sauté for 2 minutes; don't let it brown.
Add onion, zucchini, yellow squash, and 1/4 tsp.
each of the salt and pepper.
Cook until squash is tender, about 15 minutes.
Divide the mixture in half.3.
Mix the mayonnaise and cheeses and set aside.
Layer the sliced tomatoes in the bottom of the baked piecrusts.
Sprinkle the tomatoes with the remaining salt and pepper.
Layer the squash mixture on top of the tomatoes, then layer the water chestnuts.
Top each pie with half of the mayonnaise and cheese mixture.
Bake, uncovered, for 40 minutes.
Allow the dish to stand for 15 minutes before cutting into wedges.