Lightly spray or grease a casserole dish that is 22 x 33 cm (9 x 13 inch); set aside.
Empty jar of ground beef into a microwave-safe vessel. If using home-canned mushrooms (optional), open their jar and add them, too. Zap in microwave for a minute or two to heat. Remove, drain through a sieve for a minute or two.
When beef is drained, stir in the taco seasoning and the salsa. Set aside.
Wash peppers and onion (seed peppers; peel onion.) Chop, and set aside, combined.
Wash and chop green onion. Set aside separately.
Mix up DIY biscuit mix according to directions for that mix.
Place half the prepared biscuit dough in scattered dollops over the bottom of the casserole dish.
Scatter with half the meat mixture, half the pepper mixture, and half the cheese.
Repeat for second layer.
Scatter the green onion on top.
Cover with tin foil and put in oven for 35 minutes.
Remove foil, return to oven for 15 minutes.
Remove from oven, let stand 5 minutes.
Garnish servings with fat-free sour cream (optional.)