Place your chopping board and cut the onion into half moon slices. In a pan add 2 tsp olive oil. When the oil is hot enough add the onion and cook stirring occasionally until softened and slightly caramelized. Set it in a bowl for later.

Chop the mushrooms in small pieces. Using the same pan add the rest of the olive oil. Add the mushrooms in the pan and cook until they get a golden color. Add the previously minced garlic, cook shortly and pour the mixture in the same bowl with the onion. In the bowl add the thyme, salt, vinegar and previously crumbled goat cheese. Stir all the ingredients with a spoon and the filling is ready.

Cut the bread into 4 smaller pieces and every piece in half so you can fill it. Drizzle every piece of bread with oil and balsamic vinegar. Cut the focaccia horizontally. Brush the insides lightly with olive oil and balsamic vinegar. Add a few spoons of mushroom mixture in the middle of the sandwich and spread onto the bottom of the bread. Add a pinch of black pepper, a few slices of sun dried tomatoes and some spinach leaves. Adjust the top of the sandwich and repeat the same procedure for all the sandwiches.

Place the panini on a panini press (you can also use a pan and place something heavy over it) Toast for a few minutes until the bread gets crispy and enjoy.