Spinach Pierogi Pizza

• 10 pillsbury
• 220 gr mashed potatoes
• 110 gr mozzarella (shredded)
• 60 gr onion (chopped)
• 55 gr cheddar cheese (shredded)
• 34 gr pkg green giant harvest spinach (fresh frozen)
• 9 gr butter
• 10 ml oil
• 1 gr garlic salt
• 1 slice onion