Preheat the oven to 350°F.
Rub the bread slices with the cut side of the garlic clove and slice the bread into cubes.
Spritz the bread cubes with olive oil and bake until crispy, 10 to 15 minutes.
Make the dressing: In a high-speed blender, place the cashews, garlic, lemon juice, mustard, capers, water, and a few grinds of black pepper. Blend until creamy.
Preheat a grill or grill pan to high.
Slice the romaine heads in half lengthwise, then drizzle with a bit of olive oil and pinches of salt and pepper.
Grill the romaine, cut-side down, until char marks form, 1 to 2 minutes. Gently flip the romaine and grill for 2 minutes more.
Assemble the salads with the grilled romaine and a drizzle of the dressing.
Top with the radishes, chives, capers, and croutons.
Sprinkle with the hemp seeds, microgreens, and red pepper flakes, if using.
Serve with the lemon wedges and the remaining dressing on the side.