In a large skillet, heat olive oil over medium heat. Brown the sausages on all sides (about 5 minutes).
Place sliced onions, peppers, and minced garlic at the bottom of the crockpot.
Lay the browned sausages on top of the vegetables.
Pour diced tomatoes over the sausages and sprinkle with oregano, basil, salt, and pepper.
Cover and cook on LOW for 6-7 hours or HIGH for 3-4 hours until sausages are cooked through and vegetables are tender.
Serve over hoagie rolls or cooked pasta. Enjoy!