Mim's Mexican Chicken

• 1 onion (chopped)
• 1 freezer bag (jumbo)
• 300 ml milk
• 280 gr chicken (cooked)
• 160 gr cheddar cheese (grated)
• 1 package corn tortillas
• 1 package cream of chicken soup condensed
• 1 package cheddar cheese soup condensed
• 1 package tomatoes with green chilis