For The Taco Meat: Heat a large skillet over medium/high heat. Cook and crumble the ground meat until no pink remains, drain off any fat. Add in spices with 1/4-cup of water. Mix thoroughly and cook until most of the water has evaporated and meat and spices are well combined.
For The Guacamole: Slice open, seed, and scoop out the avocado halves into a small bowl. Add lime juice and mash with a fork. Stir in chopped onion, cilantro, and a good pinch of salt. Use immediately.
Assembling the sandwiches: Heat a large skillet over low heat. Butter the slices of bread and start layering the sandwiches – buttered sides facing out. Start with about 1 ounce of cheddar; top with about 1/4 cup of taco meat, then a 1/4 cup of guacamole; layer a few tomato slices; top with 1 ounce of Monterrey Jack; finish with your top piece of bread. Grill on low for 4-5 minutes or until golden brown, flip and finish the other side for an additional 4-5 minutes. Serve with sour cream, salsa, and any extra guacamole for dipping.