Add 1 tbsp veg. oil to a heavy skillet on simmer or very low heat, add onions and stir to lightly coat with oil. Sprinkle lightly with salt, 1/4 tsp. Cook stirring every 5 minutes until opaque and lightly browned, 30 to 45 minutes. Remove the onions and keep warm.
Wipe the skillet clean then add 1 tbsp veg. oil heat on med. high to high heat, add the sliced mushrooms, and 1/4 tsp. salt. Cook, turning occasionally until browned, 6 to 8 mins. Remove from the heat and allow to cool slightly, then add garlic and 1 tbsp chopped parsley, stir in, 1 minute. Remove mushrooms, chop into small pieces, and keep warm.
Wipe out the skillet again and put on stove on medium heat. Very lightly brush olive oil on both sides of the bread and place in the skillet, (2 batches). Toast the first side, about 2 minutes, turn to toast the second side.
Spread the crostinis with cream cheese. Use your fingers or a fork to add caramelized onion, then add mushroom pieces. Sprinkle with the remaining parsley. Serve warm.