In a small bowl, whisk together the vinegar, sugar, and salt until dissolved. Add sliced jalapeños and a sprinkle of chopped cilantro, ensuring they are fully submerged in the liquid. Set aside to marinate for about 10 minutes.

Combine the thinly sliced red onion with lime juice and zest and a pinch of salt. Massage the onions for 2-3 minutes until softened and infused with lime. Let them sit to marinate.

Slice the cucumber lengthwise into quarters, then smack it with a knife or rolling pin to crack it open. Cut the cucumber into diagonal pieces.

Toss the cracked cucumber pieces with a pinch of salt and let sit for 10 minutes to draw out excess moisture. Squeeze gently to release any extra liquid before setting aside.

In a small saucepan, heat the olive oil until shimmering. Add minced garlic and cook until golden and fragrant. Let it cool, then blend with miso, vinegar, and water until smooth.

In a large bowl, combine the marinated onions, drained cucumber, cannellini beans, and chickpeas. Fold in cilantro and season with salt. Drizzle dressing and toss to combine.

Serve salad atop tostadas or as a side to grilled dishes. Store components separately in airtight containers for up to four days.