Place peppers on barbecue grill; grill over medium heat 15 to 20 minutes, turning often, until skins are blackened.
Place peppers in brown paper or plastic bag; set aside 10 minutes.
Remove skin from peppers; cut in half and discard seeds and stems.
Cut away thick ribs from insides.
Cut peppers into 1/2 in (1 cm) strips; arrange on serving platter.
In small bowl, whisk together olive oil, lemon juice, garlic, mustard, pepper and salt.
Pour dressing over peppers; sprinkle with basil leaves.