Lightly spray an 8-inch silicone tray with cooking spray.
In a bowl or glass measuring cup, beat the eggs together with the milk by whisking vigorously until the mix is frothy and light.
Fold in the chopped ham, spinach, green onion, and grated cheese, then sprinkle with salt and pepper and stir everything until well combined.
Pour the egg mixture into the greased silicone tray and spread it evenly, then arrange the sliced cherry tomatoes on top.
Heat the air fryer to 340°F (170°C) for a few minutes, then remove the basket and carefully place the silicone tray inside before putting the basket back in.
Cook the omelette in the air fryer for 9 to 12 minutes, checking after 9 minutes by gently lifting an edge to see if it has set.
If the omelette isn't fully cooked or there’s still liquid, air fry for an additional 2 to 3 minutes until it firms up.
Remove the tray carefully using oven mitts, set it on a heat-safe surface, and use a spatula to gently loosen and slide the omelette onto a plate.
Serve immediately on its own or paired with your favorite breakfast sides.