For the lime vinaigrette: In a medium bowl, whisk the olive oil, mirin, fish sauce, rice vinegar, soy sauce, sugar, lime zest and juice, and salt and pepper to taste.
For the salad: Add the rice to a dry cast-iron skillet set over medium heat and toast, stirring frequently, until nutty and fragrant, 10 to 12 minutes. Transfer to a bowl to cool. Place the rice in a spice grinder and pulse until finely ground (the size of kosher salt). Set aside.
Heat the sesame oil in a saute pan over high heat. Add the green beans and cook until well charred on the outside, about 2 minutes. Transfer to a plate and set aside. (The beans should still be almost raw in the middle so they remain crunchy.) Place the cherry tomatoes in the same pan and lightly char; transfer to the plate with the beans and let cool. Cut the tomatoes in half (it's okay if they get a little smashed), and cut the beans into 2-inch-long pieces.
In a large bowl, combine the green beans, tomatoes, mung beans, red onions, scallions, papayas, Thai bird chiles, red peppers, cucumbers, basil, mint, pepitas, 1/2 teaspoon salt and pinch of pepper. Drizzle with the lime vinaigrette and mix well. Transfer the salad to a large serving platter and garnish with the toasted ground rice (for fragrance and a crunchy texture).