Butter the bread thickly on both sides and toast in a hot frying pan until golden and crisp. Halve the avocado and use a spoon to scoop out curls of flesh, layering them on the bread. Season with salt and chile powder to taste. Squeeze the lime over the top and garnish with fresh herbs.
*Buy at an Asian grocery store or online, or make it yourself: Toast a few dried bird's-eye or arbol chiles in a dry frying pan over medium-high heat, turning often, until toasted, 1 to 3 minutes depending on size. Let cool, then grind in a spice grinder or use a mortar and pestle.
Note: Nutritional analysis is per toast.