Start by heating oven to 350. Brush corn tortillas with olive oil on both sides. Place in oven and cook about 5 minutes per side. Or until almost crisp!
Meanwhile, make the sauce! In a small sauce pot add in olive oil, onion, tomato paste, chilies. Cook down about 3 minutes until onions are cooked through. Add in water. Bring to boil and simmer another 3 minutes. Pour sauce in a blender and blend until smooth.
Start assembling pizzas! Place 1 tbsp refried beans on the bottom of 2 tostadas. Then add a layer of beef. Place back in oven for about 5 minutes or until warmed through.
Remove from oven and top with second tostada. Add a layer of sauce and a good amount of cheese! Add back into the oven and broil until cheese is melted!
Garnish with more sauce, sour cream and cilantro!!