Heat oil in an 8″ cast iron skillet over medium heat then sauté onions for 4 minutes. While the onions are sautéing, cook spinach in boiling water for 30 seconds then remove from heat, rinse with cold water and squeeze to remove excess water.
Add jalapeño, half of the bacon and garlic to onions and sauté for another minute.
Turn off the heat then add the rest of the ingredients, except the other half of the bacon, and mix well. Top with the bacon then bake for 20 minutes. Broil on high to brown the top if desired.
Serve with chopped veggies, grain-free tortilla chips or just eat it by the spoonful!