Heat 1 and 1/2 Tbsp olive oil in a skillet over medium heat. Add sliced onions and sprinkle with 1 tsp salt. Cook on medium heat stirring frequently until the liquid evaporates and the onions are golden. Continue cooking until the onions are about half the size as they were when they began cooking. Add splashes in the pan if they begin to burn. When caramelized, set aside. 

Heat the remaining olive oil in a skillet over medium heat. Add sliced mushrooms, remaining salt, pepper, and garlic powder. Stir frequently until the liquid has evaporated and the mushrooms have a golden sear. Set aside. 

Preheat oven to 350 degrees or heat up panini press to a medium-high heat.

Spread 1/2 the pesto on each half of the baguette. On the top half, over lay the tomato slices and 3/4 of the cheese. 

On the bottom half, cover with remaining cheese followed by onions, mushrooms, and artichokes. Put the two halves together. 

Toast in a 350-degree oven for 10 minutes or heat a panini press to medium-high heat and cook until cheese melts. Cut sandwich into four pieces, each person receiving 1/2 the baguette.  Serve warm.