Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper.
Place the cubed butternut squash on the baking sheet and toss with 0.5 tsp of olive oil and half of the sea salt and black pepper.
Spread the squash into a single layer and roast for 15 minutes.
While the squash is roasting, pat the salmon fillet dry and season the top with dried thyme, dried rosemary, garlic powder, and the remaining sea salt and black pepper.
Remove the baking sheet from the oven, move the squash to one side, and place the salmon fillet on the other side.
Drizzle the salmon with the lemon juice and the remaining 0.5 tsp of olive oil.
Return the pan to the oven and roast for an additional 12 to 15 minutes until the salmon flakes easily with a fork and the squash is tender.
Place the fresh baby spinach on a plate and top with the hot roasted squash to slightly wilt the greens, then serve the herb-crusted salmon alongside.