Inspect and scrub clams under cold running water, discarding any with cracked shells or that remain open when tapped.
Place scrubbed clams in a bowl of cold salted water and let sit for 20 minutes to expel any sand, then drain and rinse thoroughly.
While clams soak, halve cherry tomatoes and finely chop onion; set aside separately.
Toast garlic bread slices until crisp and golden; reserve for serving.
Heat olive oil in a wide, heavy pan over medium heat.
Add finely chopped onion to the pan and sauté for 2–3 minutes until softened and translucent, not browned.
Add red pepper flakes to taste and cook for 30 seconds to bloom the aroma.
Add halved cherry tomatoes to the onions, season lightly with salt and pepper, and cook, stirring, for 4–5 minutes until tomatoes start to soften and release their juices.
Pour in dry white wine and bring to a simmer, allowing alcohol to evaporate and flavors concentrate for 2 minutes.
Increase heat to medium-high, add drained clams to the pan, and cover tightly with a lid.
Steam clams for 3–5 minutes, shaking the pan occasionally, until clams have opened; discard any clams that do not open.
Remove pan from heat and stir in freshly chopped parsley.
Taste the sauce and adjust salt and pepper if necessary.
Divide clams and tomato sauce evenly among shallow bowls.
Drizzle any pan juices over the clams.
Serve immediately with toasted garlic bread on the side for dipping.