Roast the peppers:
Set the broiler rack on the top rung and heat the broiler. Lightly oil a broiling pan. Set the pepper halves on the pan, cut side down, and flatten them with your palm. Broil until the skins blister and blacken, 10 to 15 minutes. Seal the peppers in a paper bag (or put them in a large bowl and cover it) so the peppers steam and the skins loosen.
When the peppers are cool enough to handle, peel away the blackened skin and discard it. (It helps to rinse your hands occasionally as you do this, but don’t rinse the peppers or you’ll dilute their flavor.)
Make the gazpacho:
Put the peppers and tomatoes in a food processor and pulse to chop them finely (or use a knife). Put them into a large bowl and stir in the garlic. Gradually stir in the olive oil to incorporate it. Add the lemon juice, scallions, cucumber, and all but 2 tsp. of the herbs (reserve these for the shrimp or goat cheese; if you’re not adding either of these garnishes, mix in all the herbs now). Taste, season the soup well with salt and pepper, taste again, and add more drops of olive oil or lemon juice, if you like. Cover and chill.
If using the goat cheese, put it in a bowl and sprinkle generously with olive oil, the reserved fresh herbs, and pepper to taste; toss gently with a rubber spatula. If using the shrimp, put it in a bowl, moisten with olive oil, and add the reserved fresh herbs and salt and pepper to taste; toss with a rubber spatula.
Taste the gazpacho again and adjust the seasonings if necessary. Serve in chilled soup bowls, garnished with either the goat cheese or shrimp, if using, or just a little spoonful of olive oil floating on top.