Boil your 1# box of Shells according to the directions on the box. Drain noodle. Put the noodles inside of a 9 x 13 Glass pan.
Dice 1 Large onion and sau'tee in a pan with a tab of butter. Mix it into the Shell noodles. Salt & Pepper to taste.
Open can of diced tomatoes. Drain most of the juice from it. Now, Mix the tomatoes into the Shell Noodles.
Cut Velveta into Squares (save 3 slices whole to the side). Slowly melt into the cup of Milk in a sauce pan. When completely melted pour over noodles. Mixing it well. Make sure it is completely covered.
Make sure all the liquid Cheese is mixed well and completely covers the noodles. Carefully slice the 3 remaining cheese slices and place them on top.
Pre-Heat over to 350 and Bake it until lightly golden brown on top. Roughly an hour.
Remove from oven let it sit for 5 mins then ENJOY!