Preheat the oven to 375 degrees. Line a rimmed baking sheet with unbleached parchment paper. Toss the quinoa with 1 Tablespoon of olive oil and spread quinoa evenly over the baking sheet. Bake in oven for 10 -15 minutes or until crispy. Set aside to cool.
Segment grapefruit (see my blogpost on segmenting citrus). Squeeze membranes into a measuring cup and add enough rice vinegar to the juice to total 1/3 cup. Set aside.
Make vinaigrette: in a blender, combine grapefruit juice-rice vinegar mixture, shallot, garlic, mint leaves, jalapeño (if using), salt and pepper. While the blender is running, slowly pour in the oil and process until completely smooth.
Assemble salad: Place greens on a platter and toss with enough dressing to coat lightly. Sprinkle with crispy quinoa. Arrange the grapefruit, avocado and radishes on top and drizzle with some more dressing. Top with sprouts if desired and a sprinkle of flaky salt.