To make the gnocchi: In a large-size bowl, stir together the ricotta, eggs, Parmesan cheese, salt, white pepper, and garlic powder until evenly combined.
Mix in the almond flour, arrowroot starch, and ¼ cup of the tapioca starch to form a soft dough. Add more of the remaining ¼ cup tapioca starch as needed.
Line a baking sheet with waxed paper and lightly dust with tapioca starch. Divide the dough into 4 equal pieces. On a surface dusted with tapioca starch, roll each piece into a ½-inch thick rope. Cut each rope into 1-inch pieces and place on the prepared baking sheet. Place the gnocchi in the refrigerator until ready to cook.
Bring a large-size pot of lightly salted water to a boil over high heat. Boil the gnocchi, in batches if necessary, until they float to the surface, 1 to 2 minutes. Drain or remove from the water with a skimmer.
To make the sauté: In a large-size skillet over medium heat, melt the butter. Sauté the garlic until fragrant, about 1 minute. Add the cooked gnocchi, spinach, and tomatoes. Cook, stirring, for 2 to 3 minutes, or until heated through and combined. Sprinkle with the feta cheese just before serving.