Fill a medium-sized saucepan with water and place it on the stove over medium-high heat to boil. Add salt to the water.
While the water is on the stove, chop up the bell pepper, onion, and garlic.
Put the canned whole tomatoes and tomato paste into a medium-sized sauce pan. Mash the whole tomatoes and the tomato paste together. Place the saucepan over medium heat. Once it is warm, reduce to medium-low heat.
Once the water has boiled, add shells, stir them, and cook for 10 minutes or are al dente.
Add chopped bell pepper, garlic, onions, and thyme into the saucepan with the tomato mixture until the vegetables until the bell pepper pieces are softer and onion pieces are translucent.
While the vegetables are blending in the saucepan, brown the ground chicken in a pan. If it is not a non-stick pan, add a bit of oil to the pan before adding the meat so it will not stick to the bottom. Drain fat from the meat once it has been cooked.
Add cooked ground chicken to the tomato sauce and cook for about 10 minutes. Add salt and pepper to taste. Stir occasionally.
Once the shell noodles are cooked, drain the water away from the shells and place into an 8x8x8 casserole dish.
Add the cooked sauce on top of the shell noodles. Shake the casserole dish to get the sauce to blend into the shells.
Add the mozzarella cheese on top of the shell noodles and the meat sauce.
Move the rack in the oven to the top level and set it to broil. Place the casserole dish in the oven until the cheese is a golden brown.
Remove the casserole dish from the oven and serve.