Preheat oven to 400°F. Wrap beets in foil and roast on a small baking sheet until a paring knife slides easily into center, 45 to 50 minutes. Carefully unwrap and set aside until cool enough to handle. Slide skins off beets under cold running water. Thinly slice and drizzle with 2 tsp lemon juice; set aside.Meanwhile, in a small saucepan, combine vinegar, cane juice, coriander seeds, garlic, salt, bay leaf and 1/2 cup water; bring to a boil, stirring until cane juice is dissolved. Stir in onion and remove from heat; set aside to cool for 15 minutes. Drain.Meanwhile, in a medium bowl, combine shrimp, yogurt, dill, mayonnaise, lemon zest, remaining 4 tsp lemon juice and pepper.Place 1 lettuce leaf on each slice toast; top with sliced beets, shrimp mixture and pickled onions.