Preheat the oven to 425°F. Grease a 12-cup muffin tin well.
Divide the cooked rice between the muffin cups. Spray with cooking spray Use the back of a spoon or a small measuring cup to firmly press the rice into the bottom and up the sides of each cup.
Bake for 20-25 minutes,until the rice cups are golden and crisp around the edges, 20 to 25 minutes.
While the rice cups bake, make the sauce. In a medium bowl, whisk together the soy sauce, brown sugar, 2 tablespoons water, rice vinegar, sesame oil, ginger, garlic, cornstarch, and sriracha.
Heat the avocado oil in a large skillet over medium-high heat. Add the chicken and cook, stirring often, until browned and cooked through, 7 to 8 minutes.
Pour the sauce into the skillet with the chicken and cook until thickened and glossy, about 2 minutes. Add the broccoli and toss to combine.
Fill each rice cup with the chicken mixture. Garnish with greens and toasted sesame seeds before serving.