Rinse oat groats and place into a small saucepan. Cover with water and add a pinch of salt. Cook them over medium-low heat for roughly 35 to 45 minutes or until softened (some of the groats will pop open). Remove from heat. Strain and rinse under cold water until cooled.
In a sauté pan, warm 1 tablespoon of oil over medium-low heat. Add groats to pan and cook until toasted. When fragrant and slighlty browned, remove from heat and set aside.
Peel and cut red onion into 1/2-inch rounds. Brush a small amount of oil over onions and season with a pinch of salt. Grill onions over medium heat until softened, 8 to 10 minutes. Remove from grill to cool. Reserve.
To serve salad, place spinach into a bowl or onto a platter. Top spinach with with grilled onions, marinated peppers and toasted oat groats. Season with a drizzle of your favourite oil and vinegar