Preheat the oven to 350º F. Spray with olive oil a 9 inches pie dish. Set aside.
In sauté pan over medium heat, heat the oil. When the oil is hot, add the onions. Saute for 2 minutes. Stir in the garlic and sauté for 30 sec; constantly stirring, so the garlic does not burn.
Add asparagus and mix until combine. Season the mixture with salt and pepper. Cover and let cook for 10 minutes or until the asparagus are tender. Remove from the heat and leave aside to cool.
Flake the salmon into the cooled mixture. Add queso fresco, lemon zest, eggs, and heavy cream. Season the mixture with salt and pepper and stir well to combine.
Layer 5 sheets of phyllo over the base of the prepared dish pie; lightly spray each sheet with olive oil as you place them on the dish. Make sure you fully cover the base. Overlap the rest of the sheets, one at a time, and let them hang over the edge of the pan as you layer; lightly spray each sheet with olive oil as you place them on the dish.
Add the salmon filling and distribute evenly.
Fold in the overhanging phyllo until fully cover the filling. Spray the top with olive oil.
Bake for 40 minutes or until golden brown.