Make a foil collar for the slow cooker by folding 2 18 inch long pieces of foil in half. Then fold up one long end so the collar measures 4" x 18". Line the inside of the slow cooker with foil strips.
Spray foil and bottom of 6 qt. slow cooker with cooking spray.
Cook sausage and hamburger until browned.
Add in onion and cook until softened.
Add in garlic, oregano, salt and pepper and cook for one minute.
Reduce heat to medium and add in pasta.
Cook, stirring constantly until edges of pasta begin to turn translucent, about 4 minutes.
Remove from heat and stir in tomatoes, scrap up any browned bits on bottom of pan.
Put mixture into slow cooker. Cover and cook on low for 2.5 to 3 hours or until pasta is tender.
Carefully remove foil collar and stir gently.
Top with slices or grated cheese and cover and let sit for 10-20 minutes to allow cheese to melt.