Preheat the broiler and place the whole peppers on a lightly greased tray close to the heat source until the skins are black and blistered. You can also char your peppers over a gas burner for the same result. Either way, once they are blacked and skin is charred, place directly into a heat proof bowl and cover tightly with either aluminum foil or plastic wrap. Let the peppers sweat until they are cool enough to handle. Remove aluminum foil or plastic wrap.
Carefully peel off the blackened skin, discarding the skins. Remove core and seeds from peppers. Slice lengthwise into thin, even-sized strips. Set aside.
Wash and rinse beans under cold water. Remove tops from the beans (if you desire your beans to be same size, cut them to resemble each other. I only remove tops as having them the same size is not a priority for me). Bring a pot of salted water to a boil and cook the beans for 2 minutes or until crisp tender to desired doneness (being careful not to overcook).
Drain and cool quickly by refreshing the beans under very cold water or in a bowl of ice and water. When cool, drain again. (I sometimes don't follow the cooling process as I feel it can sometimes wash the flavor away. But, if I need the cooking process to stop (because I may have overcooked them slightly), I do place them in cold water with ice cubes.
Thinly slice the onion and place in a large bowl. Add the beans and peppers.
To make the dressing, place the vinegar in a small bowl and add the oil in a thin stream, whisking constantly. Add the tarragon and cumin, and season to taste with salt and pepper.
Pour the vinaigrette onto the vegetables and toss to coat. Arrange decoratively on a platter and sprinkle with the sliced toasted almonds.
NOTE: If you can't find both yellow wax beans or yellow bell peppers in your market, you can use all green beans or all red bell peppers as I normally do. The colors are even more beautiful when you can find all the colors noted.