Place a medium sauté pan, lightly coated with olive oil, over medium high heat and sauté the onion until it is dark brown (about 5 minutes). Add the garlic, rhubarb, vinegar, brown sugar and chili flakes if using. Reduce the heat to a simmer and cook for 10 minutes until the rhubarb has softened and the liquid has reduced to a glaze.
2. Add the strawberries and mint and stir to combine. Turn off the heat and allow the strawberries to soften.