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 once 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.
Notes
The key to melting the cheese without burning the bread is the low heat setting; grill these low and slow.
Depending on the amount of filling, you may be able to get eight sandwiches in total. I made six hearty sandwiches with a little meat and guacamole leftover. Begin and end layers with cheese. They are the glue that holds the whole thing together.