Cut peppers lengthwise in half; remove stems and seeds. Place peppers on a baking sheet, skin side up. Broil 4 in. from heat until skins blister, about 5 minutes. Reduce oven temperature to 350°.
Meanwhile, in a large bowl, combine chicken, rice and pesto. When cool enough to handle, fill peppers with chicken mixture; return to baking sheet. Bake until heated through, about 5 minutes. Sprinkle with cheese; bake until cheese is melted, 3-5 minutes. If desired, sprinkle with basil.