First we sear our mushrooms. Get a pan on medium-high heat and let it get nice and hot. While your pan is heating up, cut the mushrooms into quarters (bite-sized pieces). Add your 3 tablespoons canola oil to the pan, and toss the mushrooms in. Shake pan so that each piece of mushroom gets some surface area on the pan. Season with salt and pepper.
Don't mess with the mushrooms much, let them sit and cook for 3-4 minutes. We want a hard sear, a deep brown color, this will give us lots of flavor. Repeat this process of letting the mushrooms cook for 3-4 minutes, untouched, stirring in between, for 3-4 times.
While mushrooms are searing, chop your extra firm tofu into bite-sized cubes, and slice your green onions.
Remove your mushrooms from the pan with a slotted spoon. Set aside. There will likely be some extra oil left in your pan, but if not, add a touch more. Place your two big handfuls of spinach in this hot pan. Season very lightly, and leave in pan for 15 seconds only. Take out and set aside with your mushrooms.
Assemble your salad: Mix mushrooms, spinach, green onions, and tofu together, and toss your dressing over. If you'd like, reserve some green onions to garnish with. Mix gently so you don't break up the tofu. Taste to see if you need any more salt and pepper.
Plate your salad, and top with Furikake (optional). Serve immediately while warm.