Begin by rinsing and drying the romaine lettuce leaves, making sure they remain whole and crisp for filling. Slice the cherry tomatoes in halves or quarters, depending on their size. Trim the asparagus spears and blanch or steam them just until tender-crisp, then cut them in half if desired. Thinly slice the radishes into delicate rounds to add a peppery bite.

Arrange the romaine leaves flat on a large serving platter or tray. Carefully layer each leaf with cherry tomatoes, radish slices, arugula, and tender asparagus spears, creating a colorful, garden-fresh filling.

Sprinkle the chopped walnuts generously over the vegetables, followed by sunflower seeds or your preferred seed mix for extra texture. Drizzle each boat with a light stream of olive oil and, if desired, a splash of lemon juice or a swirl of balsamic glaze to brighten the flavors. Season lightly with a pinch of salt and a few turns of freshly cracked black pepper.

Serve immediately for a crisp and refreshing appetizer, a vibrant side dish, or a nourishing light lunch.