Season the tempeh blocks on all sides with salt and black pepper, then place them in a large resealable plastic bag set inside a shallow dish to catch any potential leaks.
In a small bowl, whisk together the olive oil, lime juice, reduced-sodium soy sauce, fresh cilantro, ground cumin, and chopped chipotle pepper to create the marinade.
Pour the marinade over the tempeh in the bag. Seal the bag, removing as much air as possible, and turn it several times to ensure the tempeh is fully coated.
Refrigerate for at least 4 hours, or up to 6, turning the bag occasionally to redistribute the marinade.
Preheat your grill to medium heat.
Remove the tempeh from the bag, discarding the leftover marinade.
Place the tempeh directly on the grill rack and cook for 8 to 10 minutes, flipping once halfway through, until you have beautiful grill marks and the tempeh is heated through.
To serve, slice the grilled tempeh into four equal portions.
Top each piece with fresh avocado slices, cherry tomatoes, and an extra sprinkle of cilantro, if desired.
When handling chipotle peppers, wear gloves to protect your skin from the volatile oils. If you don't have gloves, wash your hands thoroughly with soap and warm water immediately after.
