Preheat the oven to 350 degrees F (175 degrees C). Spray the bottom and sides of a 9x13-inch baking dish with cooking spray.
Heat a large skillet over medium-high heat. Cook and stir ground beef in the hot skillet until browned and crumbly, 5 to 7 minutes. Add yellow onion, bell peppers, celery, and 1/2 of the green onion; saute until vegetables are soft, about 5 minutes. Add garlic, tomato sauce, 1/2 of the parsley, paprika, garlic powder, onion powder, red pepper flakes, meat tenderizer, salt, and pepper; cook until fragrant, about 1 minute. Stir in Worcestershire sauce and browning sauce. Drain oil and remove from the heat.
Line the prepared baking dish with refrigerated biscuits; divide them evenly and spread out to cover the pan, overlapping if necessary. Spread drained ground beef mixture evenly on top of the biscuits. Spread diced tomatoes over the beef, then evenly scatter frozen vegetables. Spread mashed potatoes over the top, and sprinkle with remaining green onions, Cheddar cheese, and remaining parsley. Cover with foil.
Bake in the preheated oven for 25 to 30 minutes. Remove foil and bake until cheese is golden and melted, another 5 minutes. Serve immediately.