1. Cut tofu into small cubes. In a large bowl, put vinegar, sugar, 1 tsp. salt and 1 cup water. Whisk to combine, then add scallions, garlic and tofu; toss gently to coat with marinade. Refrigerate for at least 15 minutes and up to 2 days.
2. Drain tofu mixture, reserving pickling liquid. In a separate large bowl, put tofu mixture and add radishes, cucumber and avocado.
3. Toss ceviche with 2 Tbsp. of reserved pickling liquid, plus oil and 1/2 tsp. pepper. Taste and adjust seasoning, adding more pickling liquid if desired. Sprinkle with cilantro and serve.