Pre-heat oven to 400 degrees. Place baking rack in a high position. 

Drizzle olive oil into pan over medium heat and add in diced onion. Let cook until translucent (about 3-4 minutes). Add salt and pepper. 

Turn heat down slightly to add in your minced garlic. Stir for about one minute, then add in spinach (can add in groups because it takes up so much room until its cooked down). Add salt and pepper.

Once spinach has wilted completely, transfer to colander in sink to let drain while you make the cheese sauce. 

In the same pan, bring milk to simmer and add in cream cheese. Stir until melted and everything is combined. Add red pepper flakes. 

Use the back of your spoon, or spatula to press the spinach mixture into the sides of the colander to release any extra water. Transfer to a cutting board along with your marinated artichoke hearts and roughly chop. 

Add spinach and artichokes to cheese sauce and combine. 

Transfer entire mixture to small baking dish and cover with shredded mozzarella cheese. Bake in 400 degree oven for 15-20 minutes on the top rack.