Heat a gas grill to high or prepare a hot charcoal fire. Brush the grill grate clean. Put the poblano directly on the grate with the lid down. Turn occasionally until the skin blackens and blisters all over. Put the poblano in a paper bag or a bowl (cover with plastic) and let cool.
Meanwhile, turn the grill burners to medium high or let the charcoal fire die down slightly. Cut the mangos in two lengthwise, slightly off center, cutting off the wide sides of the flesh from each side of the pit (you'll have some flesh left on the mango which you can snack on). Cut the peaches in quarters and pit them. Brush the cut sides of the fruit with oil and sprinkle lightly with salt. Grill the mangos and peaches cut side down until nicely marked, 2 to 4 minutes. Flip skin side down, cover and continue grilling until the juices in the fruit begin to bubble, 3 to 4 minutes. Transfer to a cutting board and cool.
Skin, seed, and roughly chop the poblano. Transfer to a medium bowl.
With a paring knife, score the mango flesh lengthwise and then crosswise, forming 1/2-inch cubes and taking care not to cut through the peel. Pop each mango half inside out to force the cubes upward and then slice the cubes free from the skin, letting them fall into the bowl with the poblano. Skin the peaches and chop into 1?2-inch pieces. Add to the mango and poblano, along with the onion, mint, lime juice, passionfruit or orange juice, and lime zest. Toss gently to mix. Season to taste with salt, pepper, more lime juice, and habanero or jalapeño (if using). Let stand at room temperature for at least 20 minutes before serving.
The salsa may be made up to 8 hours ahead; refrigerate if making more than 2 hours ahead but return to room temperature before serving.