Line a sheet pan with foil and brush it with some oil or spray it with nonstick cooking spray. Set tempeh slices out on pan in a single layer. Season tempeh on both sides with some salt and pepper. Brush the tops of tempeh slices with Honey Dijon Vinaigrette (portion for sandwiches). Transfer tempeh to the oven and bake, without turning, until tempeh is heated through and golden brown on top, 15 to 17 minutes.
While tempeh is cooking, place green beans in a microwave-safe bowl. Cover with a damp paper towel and microwave on high until tender, 3 to 4 minutes.
Toss green beans with vinaigrette (portion for green beans). Season with some salt and pepper.
Toast bread.
Assemble sandwiches by spreading mashed avocado on half the bread slices. Top with tomatoes, lettuce, tempeh, and remaining slices of bread. Serve with green beans on the side and enjoy!