Brown ground beef in pan, drain, and set aside.
Sauté onion in pan over medium heat until tender and translucent.
Add garlic and sauté until just fragrant, about 30 seconds.
Stir in tomato sauce, water, and tomato paste.
Bring to a boil, then reduce heat and simmer for 10 minutes.
Stir in thawed vegetables and 1 cup cheese and pour mixture into a greased 9 x 13 baking dish.
Top with remaining 1 cup cheese.
Remove biscuits from tube and separate each horizontally so that you have 16 thinner biscuits.
Arrange biscuits around the edge of the dish overlapping as necessary to fit them all.
In a small bowl, combine butter, oregano, and garlic powder.
Brush over tops of biscuits.
Bake at 350 for 15 - 20 minutes or until biscuits are browned on top and cooked through (gently lift one of the biscuits off of the top of the casserole to be sure it has cooked on the bottom).
Allow dish to rest 5 minutes before serving.