Preheat your oven to 400 degrees.
Combine the balsamic vinegar and 2 tbsp of olive oil. Set aside.
Wash your portobello mushrooms and remove the gills by scraping them out with a spoon. Lay them, unsliced, in a single layer in a shallow dish and pour the oil & vinegar mixture over them. Allow to rest for 15 minutes, gently spooning the marinade over them periodically.
Drain and rinse the artichoke hearts. Toss them lightly in 1 tbsp of olive oil.
Lay the marinated mushrooms and artichoke hearts out on a baking sheet. Season with salt and pepper and allow to roast for 15 minutes, flip and then roast for an additional 15 minutes. With 5 minutes remaining, add the sliced mushrooms to the sheet, drizzle with 1 tsp olive oil and season with salt & pepper).
While the mushrooms, artichokes and tomatoes are roasting, make the vegan basil pesto. You can find the recipe here.
Toast the pine nuts (see the notes in this blog post for suggestions of how to do this).
When the mushrooms, artichokes and tomatoes are done, you are ready to assemble your sandwiches. Toast your ciabatta slices just before taking the roasted vegetables out of the oven. Spread a thick layer of pesto sauce on each slice of toasted ciabatta bread, then add a layer of the roasted vegetables. Drizzle on some additional pesto sauce and sprinkle with toasted pine nuts.