Grilled Beef Tenderloin with Grilled Spring Onions

Name: Grilled Beef Tenderloin with Grilled Spring Onions
Ingredients: 1 tablespoon toasted coriander seeds; 1 tablespoon toasted cumin seeds; 1/2 tablespoon cayenne pepper; 1 beef tenderloin, trimmed (about 3 pounds); Kosher salt; Extra-virgin olive oil; 2 bunches spring onions, stems removed, cut in 1/2; Horseradish Cream, recipe follows; 1/2 cup prepared horseradish; 1/2 cup creme fraiche; 1/2 cup mayonnaise; 1 garlic clove, smashed and finely chopped; 1/2 lemon, juiced; 1 bunch chives, finely chopped; Kosher salt. if needed