To a large skillet over medium high heat, add vegan butter. When butter is melted, add hearts of palm. Saute 8-10 minutes, until golden brown.
Add red pepper, yellow onion, and garlic; continue cooking 2-3 minutes, until softened. Remove from heat.
To a medium bowl add vegan mayonnaise, lemon juice, cayenne pepper sauce, tarragon, celery, and salt and pepper, to taste. Add hearts of palm mixture and toss gently to coat.
If serving chilled, refrigerate at least one hour.
To serve, layer lettuce into toasted buns. Add hearts of palm mixture then top with a sprinkling of scallions and Old Bay seasoning.