Bring water and wild rice to a boil in a saucepan. Reduce heat to medium-low, cover, and simmer until rice is tender, 30 to 45 minutes. Drain excess liquid, fluff rice with a fork, and cook uncovered for 5 minutes more.
Preheat oven to 350 degrees F (175 degrees C).
Arrange yellow squash halves onto a baking sheet.
Bake yellow squash in preheated oven until tender, about 20 minutes.
Heat olive oil in a large skillet over medium-high heat. Saute summer squash, bell peppers, cucumbers, onion, and tomatoes in hot oil until tender, about 5 minutes.
Mound rice atop each of the squash halves. Top rice with a portion of the sauteed vegetable mixture.
Return squash to preheated oven and bake for 30 minutes more. Sprinkle Gouda cheese over the stuffed squash halves and bake until the cheese is melted, about 5 minutes.
