Preheat oven to 350F.
Heat the vegan butter in a medium saucepan over medium heat. Add the onions and garlic and cook until fragrant, about 5 minutes. Stir in the garlic powder, onion powder, mustard powder and salt. Cook for 1-2 minutes.
Stir in the diced potatoes, lentils, cashews and water. Bring to a boil, then reduce heat to medium and let simmer, covered for 15 minutes or until the potatoes are fork-tender.
Meanwhile, bring water to a boil in a medium saucepan. Cook the pasta according to package's instructions. If using broccoli or peas, add them in the last few minutes of cooking to cook until just tender, about 2-3 minutes.
Once the potatoes, cashews and lentils are done cooking, add to a blender (with its cooking water), along with the nutritional yeast and white wine vinegar. Blend until smooth, about 1-2 minutes. Taste and add more salt, nutritional yeast or spices as needed.
Pour the "cheese" over the drained pasta in its saucepan. Stir together until combined. Transfer the mac and cheese to a 12" cast-iron skillet or casserole dish.
Prepare the topping: In a small skillet, heat the vegan butter. Add the panko breadcrumbs and thyme. Toast for 3-5 minutes, stirring several times to avoid burning. You want the breadcrumbs to be lightly golden and toasted. Sprinkle the breadcrumb mixture on top of the mac and cheese.
Bake for 10 minutes at 350F.
This dish is best served immediately as the sauce thickens and it gets a little dry as it sits. But if you have leftovers, it's still good! Store it in an airtight container for up to 4 days.