Heat olive oil and butter in a skillet over medium-high heat; cook and stir onion and garlic in the hot oil-butter mixture until softened, about 3 minutes. Add squash, salt, and pepper; stir to combine. Cover skillet and cook, stirring occasionally, until squash is softened, about 5 minutes. Transfer squash mixture to a large bowl.
Mix raw almonds and 1/2 cup Colby-Monterey Jack cheese together in a bowl; stir into squash mixture. Whisk cream and eggs together in a measuring cup or small bowl; stir into squash mixture. Pour squash mixture into a 9x13-inch casserole dish; top with remaining Colby-Monterey Jack cheese and roasted almonds.
Bake in the preheated oven until casserole is golden brown and bubbling, 25 to 30 minutes.
