To me, the heart and soul of a hotdish — which my friends call ‘reverse poutine’ — is really about using what you have on hand. Whatever you choose, leave a little bite to the vegetables so you get some different textures.
Make the sauce: Heat a large skillet over medium heat and add the lemongrass, onion, galangal, ginger, garlic and lime leaves. Add the curry paste and cook, stirring, just until a fond forms on the bottom of the pan, about 2 minutes, being careful not to burn the aromatics. When the curry paste is a crimson red, stir in the roasted red peppers and tomatoes. Add the coconut milk, bring to a simmer and cook until the sauce is reduced, pale orange and bubbling, 15 to 20 minutes. Remove the lime leaves.
Carefully transfer the sauce to a blender and puree until smooth. Strain through a fine-mesh sieve and season with salt to taste. (For a thicker sauce, cook a few minutes more to further reduce.)
Make the hotdish: Preheat the oven to 425˚ F. Heat a large skillet over medium-high heat. Add the pork, season with salt and pepper and cook, breaking up the meat, until no longer pink, 4 to 5 minutes.
Meanwhile, toss the onion and root vegetables with the olive oil on a baking sheet; season with salt and pepper. Roast until just tender but still with a little bite, 12 to 15 minutes. Cut into 1/2-inch cubes.
Reduce the oven temperature to 375˚ F. In a large bowl, combine the pork, roasted vegetables and 2 cups of the curry sauce; the mixture should have the consistency of a stew. Transfer to a 3-quart casserole dish, packing the mixture down, then scatter the tater tots evenly on top.
Bake until the tater tots are golden and cooked through, about 20 minutes. Once out of the oven, top the hotdish with cilantro, scallions and lime wedges.
For an extra-crispy top, put this hotdish under the broiler for 5 minutes before serving.