Grill the vegetables. Heat a gas grill to medium-high or build a charcoal fire and let it burn until the coals are covered with white ash and quite hot. Lay the poblanos and tomatoes on the hottest part of the grill. Brush or spray both sides of the vegetable slices with oil, sprinkle both sides with salt, then lay them in a single layer on the grill.
As the poblanos and tomatoes blacken and blister underneath, turn them to blacken another part—this needs to be done over quite high heat so that their exteriors blacken before the interior becomes too soft. As the vegetable slices get richly colored underneath, flip them over to cook the other side—this can be done on a cooler part of the grill, since these vegetables need to be soft before making them into the filling.
As the vegetables are ready, remove them to a tray to cool. Rub the charred skin off of the poblanos without puncturing through the flesh, then gently slice off the indented stem ends and pull out the seed pod. Use your knife to cut open the chiles from top to the pointy ends. Rinse the chiles briefly to remove seeds and stray bits of charred skin. Pat dry with paper towels.
Pull the charred skins from the tomatoes. In a food processor, combine half of the grilled onion and the small green chiles. Pulse the processor until everything is finely chopped. Scoop in the tomatoes and less than half of the herbs, then pulse until the mixture looks like salsa. Taste and season with salt, usually about 1 ½ teaspoon.
Chop the slices of grilled vegetables into small pieces—about ¼-inch—and combine in a bowl with the cream cheese, Parmesan and remaining herbs, gently mixing until the cheeses are evenly distributed and coating the vegetables. Taste and season with salt, usually about 1 teaspoon.
Scoop a portion of the filling onto each of the poblanos, then bring the sides of the chile up over the top, reforming the chiles’ original shape and overlapping the sides slightly. Flip them over so that the seam side is down.
The chiles are delicious served at room temperature or you can warm them on the grill on a perforated grill pan or in the oven on a baking sheet. Serve with a portion of the salsa, garnished with whole herb leaves and parmesan.