Cook pasta al dente per package directions. Drain all but 1 cup of pasta water, and set aside.
Slice trumpet mushrooms to about 1/2 to 3/4 inch thickness. I kept the the tops, but you can save for another recipe if you wish.
Chop shallots and parsley and mince garlic.
In a cast iron pan or pot (this is actually easier as you'll combine everything in here at the end), add mushrooms and 2 tbsp vegan butter and sauté on medium heat until brown on both sides. You may want to do this in batches depending on the size of your pan. It's not imperative that they all get a perfect sear. You can throw them under the broiler at the end like I did. Cook them a 2-4 minutes per side, trying not to disturb them.
Remove mushrooms and set aside. In the same pan/pot, add tomatoes and another tbsp of vegan butter. Cook for about 2-3 minutes or until they begin to soften and burst (you can help them out by poking with a fork).
Add 1 more tbsp of butter and shallots. Sauté for about 2 minutes until shallots are translucent. Add garlic and sauté another 2 min.
Remove everything from pan and add vermouth (or white wine) to deglaze the pan. Simmer on medium high heat until alcohol cooks off (3-4 min). You can skip this or do it earlier (before tomatoes) if you want. I did it this way because I wanted all the flavors.
Add all ingredients back into pan/pot (except mushrooms if broiling) and toss with 1/2 cup of the reserved pasta water and lemon juice. (I saved the other half of the water for the leftovers).
Optional: Broil "scallops" until golden brown. Fold into the pasta. Garnish with fresh parsley and more lemon juice and serve.