Begin by preheating your oven to 375°F (190°C) and positioning the rack in the upper third of the oven.
In a skillet, heat oil over medium heat, then add the onions and shallots, sautéing them for about 4 minutes until they become softened and fragrant.
Introduce the garlic into the skillet and sauté for an additional 30 seconds. Once done, transfer this mixture to a bowl and set it aside for later use.
Using a food processor, blend the cream cheese, mayonnaise, artichoke hearts, and cayenne until you achieve a smooth and creamy texture.
Transfer the cream cheese mixture to a medium-sized bowl, and add the previously prepared onion mix, along with the thawed and squeezed dry spinach, and asiago cheese. Stir everything thoroughly to ensure a well-combined mixture.
Taste the mixture and add salt if necessary, though it may not be needed if using brined artichokes and cheese that is already flavorful.
Lay out 24 wonton wrappers on your kitchen counter, and place approximately 1 heaping teaspoon of the mixture onto each wonton.
Dampen the edges of the wontons with water, then carefully fold them in half to create triangular shapes, pressing the edges together to seal them securely.
Line a baking sheet with cooking spray and place the filled wontons on it. Bake them in the preheated oven for around 10 minutes, until the bottoms and edges start to turn golden brown. Flip them over and continue baking for about 4 more minutes, until both sides are crisped and slightly browned.
Serve these delicious appetizers right out of the oven for maximum enjoyment. They make a delightful and savory treat for any occasion!