In a bowl, stir together the fish sauce, chiles, and garlic. The sauce can be used immediately, but I think it tastes best if the chiles are allowed to soften and mellow for 2 to 3 hours. Store the condiment in a tightly capped glass jar in the refrigerator for up to a month, though the chiles will have lost their heat by 2 weeks.

Cut the chicken against the grain and on the diagonal into thin, bite-size slices. Set aside.

Trim about 1" off the bottom of each stalk end of Chinese broccoli. Cut each stalk on the diagonal into slices about ½"-thick and 2" long. Cut the green leafy parts crosswise into 2" pieces. Keep the stalks and leafy parts separate.

Heat the oil in a wok or a 14" skillet over high heat. When the oil is hot, add the garlic and fry for about 30 seconds, until fragrant. Add the onion wedges and let them brown on the underside, undisturbed, for 1 minute. Flip them and let brown on the second side for 1 minute. Add the chicken, tomatoes, and the stalk pieces of the Chinese broccoli and stir-fry for 3 to 4 minutes, until the chicken is cooked through.

Add the rice, sweet soy sauce, thin soy sauce, and fish sauce and stir-fry to distribute the sauces evenly and heat the rice. Make a well in the center of the rice mixture all the way to the bottom of the wok and crack the eggs into the well. Lightly scramble the eggs with the tip of the spatula, then let them cook undisturbed for about 1 minute, until they brown on one side. Add the leafy parts of the Chinese broccoli and stir-fry everything together until they are evenly distributed and the Chinese broccoli has wilted, about 1 minute. Remove the pan from the heat.

Transfer the rice to a serving platter or individual serving plates. Dust with the pepper and serve with the lime wedges, chile fish sauce, and cucumber.