Heat the olive oil in a large skillet over medium heat until it shimmers and begins to gently crackle.
Add the minced garlic to the hot oil and stir quickly, letting it cook for about 30 seconds until fragrant and golden around the edges.
Toss in the fresh spinach, handful by handful, using tongs or a spoon to coat the leaves with the garlic oil. The spinach will wilt and shrink rapidly—keep adding until all is in the pan.
Cook for 2-3 minutes, stirring occasionally, until the spinach is tender, bright green, and wilted, with the aroma of garlic filling the room.
Season with salt to taste, adding a pinch at a time, and toss in the red pepper flakes if using. Squeeze fresh lemon juice over the greens for brightness, if desired.
Remove from heat once the spinach is tender, fragrant, and glossy, and transfer to a serving dish.
Serve immediately, enjoying the tender greens with their rich garlic aroma and flavorful, earthy taste.