In a medium saucepan, combine spelt and enough water to cover by 2 inches. Bring to boiling; reduce heat. Simmer, uncovered, about 1 hour or until tender. Drain well and place spelt in a large bowl.
Add sweet pepper, cucumber, carrots, radishes, and green onions to spelt; stir to combine. In a small bowl, whisk together mayonnaise, lemon juice, salt, and cayenne pepper. Add to spelt mixture and toss to coat. Cover and refrigerate at least 1 hour or up to 6 hours.