Slice the chicken breasts diagonally into strips about 1/3-inch (1 cm) wide and place in a bowl; season lightly with salt.
Heat 2 tablespoons vegetable oil in a wok or large skillet over medium-high heat until hot.
Add the sliced onions and stir-fry for about 3 minutes, until they begin to soften and wilt.
Add the seasoned chicken strips, sliced chiles, 1/4 cup (60 ml) Thai chile jam (or 2 tablespoons paste), 1 tablespoon oyster sauce, and 1 teaspoon fish sauce to the pan.
Stir-fry everything together, tossing frequently, until the chicken is cooked through and sauces are heated, about 5 minutes more.
Remove from heat and transfer to a serving plate; adjust seasoning with salt if needed and serve immediately.