Lightly spread one side( the "outside") of each of the bread slices with olive oil (or butter), spread the other side ( the "inside" of the sandwich) with pesto.
Layer gouda and roasted beets on top of pesto.
Heat a skillet over medium-low heat ( or heat a grill pan or panini press)
Place the sandwich on the sk.illet ( or grill pan) and cook on one side until the bread is toasted and cheese is melting.
Flip sandwich over and continue cooking until cheese is melty and bread is toasty.
Open sandwich and add some fresh spinach leaves.
Let cool a few minutes before cutting.