Prep the Oven: Preheat your oven to 400°F and line a rimmed baking sheet with parchment paper.
Roast the Squash: Brush the cut sides of the spaghetti squash with 2 tablespoons of olive oil, season generously with salt, pepper, and a pinch of paprika, and place them cut-side down on the prepared baking sheet. Roast for 35 to 45 minutes until fork-tender. Cool for 5 minutes until safe to handle.
Brown the Butter& Crisp Sage: Melt the 3 tablespoons of butter in a small skillet over medium heat. Add the whole sage leaves in a single layer. Cook for 2 to 3 minutes, swirling the pan occasionally, until the butter foams, turns a rich, nutty brown with toasted specks, and the sage leaves crisp up. Immediately remove from heat, transfer the sage leaves to a paper towel with a slotted spoon, and reserve the warm brown butter in the skillet.
Make the Gremolata: In a bowl, combine the chopped parsley, marjoram, minced garlic, lemon zest, lemon juice, toasted nuts, a pinch of salt, and 1 tablespoon of the warm brown butter.
Scrape the Strands: Using a fork, gently scrape the squash flesh lengthwise into a large mixing bowl to create light, spaghetti-like strands, taking care to keep the two empty squash skins intact for serving.
Toss andRe-Stuff: Pour the remaining warm brown butter and half of the Parmigiano-Reggiano into the squash strands, tossing gently to coat. Divide the mixture and spoon it neatly back into the warm, hollowed-out squash shells.
Garnish andServe: Top each filled squash half with the marjoram gremolata, the remaining Parmesan, and the crispy fried sage leaves. Serve immediately right inside the shells.