Preheat oven to 350 F°. Line baking sheet with parchment paper.
In small bowl, combine, buckwheat, pumpkin seeds, 1 tablespoon olive oil, 1 tablespoon honey, 1/4 teaspoon hot smoked paprika, and pinch of salt. Spread mixture out on parchment paper in even layer and bake in preheated oven for 10 minutes, stirring at 4- and 8-minute marks. Remove from oven and allow to cool without stirring.
In Mason jar or small bowl, measure out 3 tablespoons olive oil. Remove 1 teaspoon and add to large bowl with kale. With clean hands, massage kale for a few minutes, working oil into kale. Set aside.
Add reserved 1/3 cup grapefruit juice to Mason jar with 1/4 teaspoon red chili flakes, 1/4 teaspoon hot smoked paprika, crushed garlic, and 1 teaspoon honey. With your hands, break up half of granola mixture and add to kale with radish microgreens, green onion, and 3 tablespoons of dressing. Toss to combine.
Arrange salad in serving bowl or platter and place grapefruit pieces overtop. Break remaining granola into bite-size chunks and add to top of salad.