Preheat your oven to 375°F and lightly grease a 9x13 inch baking dish with cooking spray or butter. While the oven heats, dice your onion into small 1/4-inch pieces and measure out all your ingredients: the ground turkey, hash browns, cheddar cheese (I recommend freshly grating your cheese from a block rather than using pre-shredded—it melts so much more evenly and creates a better texture), eggs, milk, jalapeno paste, chives, salt, and black pepper. Having everything ready before you start cooking will keep the process smooth and efficient.

Heat the avocado oil in a large skillet over medium-high heat until it shimmers. Add the ground turkey and cook for 2-3 minutes, breaking it up with a spoon as it cooks until it's mostly browned but still has a bit of moisture. Add the diced onion and cook for another 1-2 minutes, stirring frequently. Stir in 1 tablespoon of jalapeno paste and 1.5 tablespoons of chives, cooking for just 30 seconds more to bloom the flavors. I like to stop cooking the turkey while it's still slightly moist rather than cooking it completely dry—it'll finish cooking in the oven and stay more tender in the final casserole.

In a large mixing bowl, combine the seared turkey mixture from Step 2 with the hash browns, 1.75 cups of cheddar cheese, eggs, milk, remaining 1 tablespoon jalapeno paste, remaining 1.5 tablespoons chives, black pepper, and salt. Stir gently but thoroughly until everything is evenly distributed and the eggs are well incorporated—the mixture should look creamy and cohesive. Pour this entire mixture into your prepared baking dish and spread it evenly with a spatula or wooden spoon.

Cover the baking dish tightly with aluminum foil and place it in your preheated 375°F oven. Bake for 30 minutes—the foil helps the casserole cook gently and evenly while trapping steam, which keeps the egg custard moist and prevents the top from browning too quickly.

Carefully remove the baking dish from the oven and take off the foil. Sprinkle the remaining 0.75 cup of freshly grated cheddar cheese evenly over the top of the casserole. Return it to the oven uncovered and bake for another 20 minutes until the cheese is melted and the top is golden brown. The casserole is done when the center is set (it should only jiggle slightly when gently shaken) and a knife inserted in the middle comes out clean or with just a few moist crumbs.

Remove the casserole from the oven and let it rest for 10 minutes before cutting and serving. This resting time allows the egg custard to set up a bit more, making it easier to cut clean portions and ensuring the casserole holds together beautifully on the plate.