Heat an outdoor grill or a grill pan over medium-high.
Trim the ends off the eggplant, then cut lengthwise into 8 long, thin (1/8 to 1/4 inch) slices. Salt the eggplant liberally and let drain on a towel about 10 minutes; pat dry. Brush both sides of the eggplant slices with EVOO and season with pepper. Grill until tender and charred in spots, about 2 minutes per side. Transfer to a work surface.
In a small bowl, combine the ricotta, grated cheese, walnuts, thyme and lemon zest; season.
Layer each eggplant slice with the speck, then spread with the cheese mixture. Top with the greens, tomatoes and onion. Roll up, transfer to plates and drizzle with EVOO.