Add the millet to a pot and toast it for about 5 minutes, stirring occasionally. Pour in water or broth, season with salt, freshly ground pepper, add 1 teaspoon of olive oil and 1 teaspoon of lemon juice. Cover and bring to a boil.
Cook covered for about 15 minutes, until the millet absorbs all the liquid. 3 minutes before the end of cooking, add asparagus: break off the tough ends, rinse the stalks and cut into pieces. Open the pot, add brie cheese pieces if using, and cool.
Blanch the tomato, cut into cubes, place in a larger bowl. Peel the avocado, cut into cubes, season with salt and drizzle with a little lemon juice, add to the bowl with the tomatoes.
Add sliced radishes, diced sweet onion, chives, and diced chili pepper if using. Season everything with salt and freshly ground pepper and gently mix.
Mix the remaining olive oil and lemon juice with the minced garlic and add to the salad, stir well. Sprinkle with torn mint and cilantro leaves if desired.