In a pan on medium heat, add onion and some olive oil, cooking onion until beginning to soften.
Add minced garlic, cook for 1-2 minutes.
Add spinach and green onion, once spinach begins to wilt, add feta, and salt & pepper to taste, cooking for another minute or two.
Butter the outside of each slice of bread.
Spread one tablespoon of ricotta cheese on the inside of each slice.
Place spinach mixture into sandwich.
Cook sandwich until golden brown on each side.