Combine grapefruit juice, jalapeno, rice wine vinegar, sugar and salt in medium bowl. Whisk until sugar and salt are dissolved. Continue whisk while slowly streaming in extra virgin olive oil. Set aside.
Preheat oven 350°F.
Scatter pecans on a parchment paper–lined sheet tray. Roast until fragrant, about 8 minutes. Remove from oven and allow to cool completely. (Toasting nuts brings out the natural oils, giving nuts a more intense flavor.)
Meanwhile, bring a pot of water to a boil and fill a medium mixing bowl with ice water. Submerge the snap peas in the boiling water for 1 minute then, using a slotted spoon, transfer to the ice water. This softens the peas and sets their bright green color. Once peas are cool, remove from ice bath and pat dry.
In a large mixing bowl, combine kale, endives, grapefruit segments, watermelon radish, spring onions cheddar, snap peas and pecans. Dress with vinaigrette and gently toss. Divide salad among 4 plates and serve immediately.