Preheat oven to 375°F.
Heat 1 tbsp olive oil in a large skillet over medium-high heat.
Add the onion, bell pepper, and mushrooms. Cook for about 6 to 8 minutes, stirring occasionally, until softened and the mushrooms have released most of their moisture.
Add the 3 cloves minced garlic and cook for 30 to 60 seconds, just until fragrant. Remove all the veggies and put into a large bowl.
Add the fresh chicken sausage links to the same skillet and cook over medium heat, turning every few minutes so they brown on all sides. Cook until the centers reach 165°F, about 12 to 15 minutes depending on thickness.
White the sausages cook, add the cauliflower rice, onion powder, smoked paprika, Italian seasoning, salt, and pepper to the bowl with your other veggies.
Once the sausages are done, slice them into .5 inch rounds then add them to the bowl of veggies and mix together. Spread evenly into your casserole dish.
Sprinkle the 2 oz fresh grated cheddar over the top, followed by the ½ cup breadcrumbs.
Bake uncovered for 15 to 20 minutes, until everything is hot and the topping is lightly golden.
If you want the breadcrumbs extra crispy, broil for 1 to 2 minutes at the end.
Let it sit for about 5 minutes before serving.