Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease it with cooking spray and set aside.

In a skillet, heat olive oil over medium heat. Add chopped onion and minced garlic, and sauté until translucent and fragrant, about 2-3 minutes. Add chopped spinach and cook until wilted, stirring occasionally, for another 2-3 minutes. Remove from heat and let it cool slightly.

In a mixing bowl, combine the cooked spinach mixture with full-fat ricotta cheese, grated Parmesan cheese, salt, and pepper. Mix well until all ingredients are thoroughly incorporated.

In a microwave-safe bowl, combine the shredded mozzarella cheese and cream cheese. Microwave on high for 1 minute, then stir. Microwave for an additional 30 seconds, and stir until smooth.

Add almond flour, egg, and baking powder to the cheese mixture. Mix until a dough forms.

Place the dough between two sheets of parchment paper and roll it out to about ¼ inch thickness. Cut the dough into squares or rectangles.

Spoon a generous amount of the spinach mixture onto one half of each dough square or rectangle, leaving a small border around the edges.

Fold the other half of the dough over the filling to create a pocket or triangle shape. Use a fork to press down the edges and seal the pastry.

Place the stuffed pastries on the prepared baking sheet. Lightly spray the tops with cooking spray to help them brown evenly. Bake in the preheated oven for 15-20 minutes, or until the pastries are golden brown and puffed up.

Remove the pastries from the oven and let them cool for a few minutes before serving.

Enjoy these keto spinach stuffed pastries warm as a delightful appetizer, side dish, or even a light meal.