Preheat the oven to 400ºF and cut two pieces of tin foil for the beets, garlic, and onion.
Place the beets in a piece of tin foil and drizzle them with 2 teaspoons of olive oil and season with ¼ teaspoon salt and ¼ teaspoon pepper. Seal the tin foil tight so no heat can escape.
Next, place the garlic and onion in a piece of tin foil, drizzle with 2 teaspoons olive oil and ¼ teaspoon of salt, and ¼ teaspoon of pepper, and seal so no heat can escape.
Transfer the beets, garlic, and onion to a baking sheet and bake for 30-40 minutes or until the beets are fork-tender and the garlic is soft.
While the vegetables are roasting, bring a large pot of salted water to a boil and cook the bucatini until al dente. Set aside 1 cup of pasta water for later (we take out more than we need just in case). Strain the pasta and set aside.
When the vegetables are done roasting, carefully peel the beets and transfer them to a high-speed blender along with the onion. Carefully squeeze the garlic cloves out of the garlic wrapper into the blender.
Add the rest of the olive oil, 2 oz. of goat cheese, the rest of the salt, and 4 tablespoons of starchy pasta water to the blender and blend all of the ingredients together until smooth. Taste test the sauce and add more salt if needed.
If the sauce is still hot, add the sauce and cooked pasta to a large bowl and mix. If the sauce needs to be warmed up, transfer the sauce to a saucepan and heat over medium heat until it reaches the desired temperature.
When the sauce and pasta are combined, top with the remaining goat cheese, pistachios, dill, lemon zest, and flakey salt. Serve immediately.