Drizzle brown rice vinegar over cooked black rice in a medium bowl, mix to coat evenly.
Warm coconut oil in a large frying pan over medium heat. Add asparagus to the pan, followed by a pinch of salt and black pepper and saute for about 5 minutes, until bright green and crisp-tender.
Slice each avocado quarter into three wedges. Squeeze lemon or lime juice over the avocado to prevent discoloration.
Place one nori sheet at a time on a sushi mat or a cutting board, shiny side down and lines going horizontally. Measure ¾ cup of black rice and cover the nori with it evenly, leaving a 1-inch border at the side opposite to you, parallel to the horizontal lines of the nori. Wet your hands to prevent rice from sticking to them when distributing.
Arrange 3 avocado wedges along the side of nori closest to you, slightly overlapping them. Top with about 5-6 strawberry slices, overlapping those as well. Place 2 asparagus spears next to strawberry slices, tips facing the edges, followed by a few spinach leaves.
Lightly moisten the uncovered border of the nori with water. Start rolling by folding the end of nori closest to you over the filling, squeezing firmly, and continue rolling to the end. The moistened border will stick and seal the roll. Wrap the sushi mat around the roll and squeeze gently to form the roll into its final shape. If not using a mat, squeeze with your hands to stabilize. Put the roll aside, seam-side down, and repeat with the rest of nori sheets and filling ingredients.
Place one roll at a time on a cutting board and slice in half with a sharp, moistened knife. Then cut each piece in half again, wiping the knife in between cuts if necessary, and repeat by cutting each of the 4 pieces in half one last time. You should have 8 pieces. Serve immediately with tamari.
Recipe by Golubka Kitchen at https://golubkakitchen.com/strawberry-and-asparagus-black-rice-sushi/