Press and slice the tofu: Wrap the 300 g block of firm tofu in a clean kitchen towel or paper towels and press under a weighted baking sheet or plates for 10–15 minutes. Pressing removes excess water so the tofu will absorb the miso marinade and develop a golden sear rather than steam when it hits the pan.

Make the marinade while the tofu presses: In a shallow dish whisk together 2 tsp white miso paste, 2 tsp low-sodium soy sauce and 2 tsp rice vinegar until smooth. The miso provides deep umami and a touch of sweetness; the soy adds salt and the vinegar brightens the flavor and helps tenderize the tofu surface so the miso adheres.

Slice the pressed tofu into 6–8 mm thick slabs (about 4 slices). Pat them dry again lightly and place them in the marinade, turning to coat both sides. Let them sit for 8–12 minutes while you prep the rest — short marination is enough because the miso sits on the surface and gives concentrated flavor.

Quick-pickle the red onion: Thinly slice enough red onion to make 40 g, then toss with 2 tsp rice vinegar (1 tsp per person) and a pinch of salt in a small bowl. Let sit 5–10 minutes; the vinegar softens the bite and gives bright acidity that cuts the richness of the avocado and miso. Keep refrigerated if you make it earlier.

Prep the remaining garnishes: Slice the avocado, wash and pat-dry the baby kale, chop the cilantro or chives, and toast 2 tsp sesame seeds in a dry pan over medium heat for 30–60 seconds until fragrant (watch closely — they burn fast). Toasting sesame seeds unlocks their nutty aroma and adds depth.

Heat the pan: Place a large nonstick or stainless-steel skillet over medium-high heat and add 2 tbsp olive oil. Heat until shimmering but not smoking — hot oil ensures a quick Maillard reaction (browning) on the tofu surface for flavor and texture.

Sear the tofu: Remove excess marinade from the tofu by letting extra drip off (don’t wipe all of it away). Add the slabs to the hot pan in a single layer (do not overcrowd). Sear 3–4 minutes per side until a deep golden-brown crust forms. Resist flipping too often — a steady sear builds color and savory flavor.

Finish with lemon and seasoning: After the tofu is browned, squeeze half the fresh lemon (about 1 tbsp) over the pieces and season lightly with salt and pepper. The lemon adds a bright counterpoint to the miso’s richness and lifts the overall dish.

Toast the sourdough: While the tofu sears, toast 4 slices of sourdough until crisp and golden, either in a toaster or under a broiler brushed lightly with oil. A crunchy base holds the toppings and contrasts the soft avocado and tofu.

Assemble the toasts: Lay the toasted sourdough slices on a board. On each slice, arrange a small handful (about 20 g per toast) of baby kale, then a layer of sliced avocado (season avocado lightly with a pinch of salt and a drizzle of lemon). Place one or two slices of miso-tofu on top, then scatter the quick-pickled red onion and toasted sesame seeds. Finish with chopped cilantro or chives and a final squeeze of lemon if desired.

Serve immediately: Serve the toasts while the tofu is warm and crusty and the bread is still crisp — this maximizes contrast among textures. Offer extra sesame seeds and lemon on the side.