To make the cheese sauce: In large saucepan, melt butter over medium-high heat. Add garlic and onion and sprinkle flour over the mixture. Cook, stirring occasionally, for 3 minutes, until onion and garlic smell fragrant and flour evenly coats the vegetables. Slowly whisk in the heavy cream and bring to a simmer. Add sambal and hot sauce, reduce heat to low, and simmer for 5 minutes. Slowly whisk in cheese, then season to taste with salt and pepper. Set aside.
To make the casserole: Preheat oven to 450 degrees. Place poblanos on a rimmed baking sheet and drizzle oil over them. Use your hands to coat the chiles well. Season chiles with salt and pepper and roast, turning once, until the skins are blistered, about 15 minutes. Transfer the peppers to a heatproof bowl, cover with plastic wrap and let sit for 10 minutes to steam. Meanwhile, reduce oven to 350 degrees. Using a paper towel, gently rub the skins off the chiles. Remove the stems and seeds, then roughly chop the peppers.
In large bowl, combine frozen Tater Tots, cheese sauce, half of the Cheddar cheese, the poblanos and half of the pickled jalapeños. Season with salt and pepper, and mix thoroughly.
Grease a 9- by 13-inch casserole dish and pour the tater tot mixture in. Top with remaining cheese and jalapeños. Bake until golden brown and bubbling, 25 to 30 minutes. Serve hot.