Yes, it’s possible to bulk up on tofu. A joint research study by Canadian and Brazilian scientists, presented at the 2019 American College of Sports Medicine annual meeting, discovered no difference with respect to lean body mass and muscle strength gains between 19 vegan and 19 omnivorous young men enrolled in a 12-week, twice-weekly program of resistance training. During the intervention, each participant consumed 1.6 grams of protein per kilogram of body weight per day, either solely from plants or from a mix of plants and animals.
For gaining muscle, protein quality differences among foods (for example, dairy is higher-quality than beans) seem to matter less than simply getting sufficient protein each day.
The tricky part for vegan weightlifters is making sure they eat enough protein in the absence of meat and dairy, since weightlifters need to consume about double the 0.8 g/kg/d recommended for sedentary people.