Make the sauce. In a small sauce pan, mix together the soy sauce, Sriracha, honey, garlic, corn starch and two tablespoons water. Cook over medium heat, stirring often, until thick and clear. Lower the heat and simmer for another two to three minutes. Turn off the heat. Stir in the lemon juice and sesame seed oil. Set aside.
In a large mixing bowl, whisk the starch, flour, salt and pepper. Stir in enough iced water to make a thick but still pourable batter. Dump the cauliflower florets into the batter and mix to coat each piece well.
In a wok or frying pan, heat enough cooking oil to reach a depth of at least two inches. Over medium-high heat, cook the Drop the battered cauliflower one by one into the hot oil and cook, flipping midway through the cooking if necessary, until lightly browned and crisp. If your wok or frying pan is rather small, cook the cauliflower in two to three batches to avoid overcrowding. Scoop out the cauliflower and drain on stack of paper towels.
Transfer the cauliflower to a large mixing bowl. Pour in the sauce. Toss until every floret is glazed and shiny.
Transfer the soy chili honey garlic cauliflower to a serving plate or shallow bowl (or in individual bowls or plates). Garnish with sliced scallions and serve.