Bake bacon in the preheated oven until partially cooked but still flexible, 6 to 8 minutes.
Brush venison tenderloins with olive oil and season with onion powder, salt, and black pepper. Place tenderloin roasts side by side and wrap them together in strips of partially cooked bacon. Place into a roasting pan.
Roast until bacon is browned and an instant-read meat thermometer inserted into the thickest part of a tenderloin reads at least 145 degrees F (65 degrees C), about 1 hour.
Heat butter in a saucepan over medium heat; cook and stir mushrooms and garlic in hot butter until mushrooms are soft, 8 to 10 minutes. Stir green onion into mushroom mixture; pour in cream. Cook, stirring often, until sauce is heated through. Serve sauce with tenderloins.