1Preheat oven to 375 degrees. Grease a 9x9" baking dish for the casserole. Use a different pan for baking the squash.
2With sharp knife slice top out of squash. Stand squash flat on the cut side. Slice squash in half. NOTE: this squash was not easy to cut, pretty tough skin.
3Scoop out the seed and membrane.
4Brush inside of each half with oil; sprinkle with salt an pepper. Place cut sides down in baking pan.
5Bake for about 40 minutes or until squash is fork tender.
6Remove from oven; let cool for about 10 minutes or until cool enough to handle.
7REDUCE oven heat to 350 degrees.
8Using a fork, scrape out the spaghetti squash. Place in bottom of prepared baking dish. Sprinkle with salt and pepper and a small amount of the taco seasoning; toss. Spread squash evenly over bottom of baking dish.
9In large skillet over medium heat, cook meat, onion, pepper, and garlic until meat is cooked. Add taco seasoning and add salt and pepper to taste. Add pepper flakes for a little more heat. Stir in refried beans and black beans. Remove from heat.
10Layer beef mixture over squash.
11Drain some of the liquid from Rotel tomatoes. Spread tomatoes evenly over top of meat layer using about 2 tbsp. of the liquid.
12Bake for 40 minutes or until bubbly. Remove from oven; sprinkle cheese evenly over top. Return to oven and bake a few more minutes until cheese has melted.