Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Slice the tempeh into thin strips and slice the zucchini and bell peppers into bite-sized pieces.
In a bowl, toss the tempeh, zucchini, and bell peppers with olive oil, sea salt, black pepper, and garlic powder until evenly coated.
Spread the mixture in a single layer on the prepared baking sheet and roast for 20 minutes, flipping halfway through, until the tempeh is golden and veggies are tender.
While the vegetables roast, toast the sprouted grain bread slices until they reach your desired level of crispness.
Spread the hummus evenly across one side of each bread slice.
Layer the roasted tempeh and vegetables onto one slice of bread, top with fresh baby spinach, and close the sandwich with the remaining slice.
Slice the sandwich diagonally and serve immediately while the filling is warm.