Rinse the fish and pat dry. Using a sharp serrated knife, make 3-4 vertical cuts along each side (see photo). Though not authentic, you can remove the head and tail if desired.
Squeeze about 1 Tbsp. of lime juice over the fish, then sprinkle salt over. Be sure to do both sides. Set aside while you prepare the sauce.
Place all sauce ingredients in a food processor or mini-chopper and process until you have a beautiful bright green paste-like sauce. (You can also use a pestle & mortar for this task, adding the liquid ingredients afterward.)
Taste-test the sauce, adding more fish sauce if not salty enough, more sugar if too sour, or more chili/chili sauce if not spicy enough.
Pour sauce into a sauce pan and set aside until later.
Spread flour over a plate or other clean surface. Then dredge the fish in it, turning until it's well coated. Set fish beside the stove, along with tongs and a little absorbent paper or clean tea towel.
Pour enough oil into a wok or large frying pan (large enough for the fish) so that oil is at least 1 inch deep. Turn heat on high. When you see bubbles forming on the bottom of the pan, test it by dropping in a small cube of bread - if it begins to sizzle and turn brown, it's ready. If not, the oil needs longer to heat up. When hot enough, carefully place fish in the oil. Turn the heat down to medium, or just above medium.
Allow fish to cook at least 3 minutes per side before disturbing or turning it (this will prevent the skin from tearing). Depending on how thick your fish is, it will take 8-12 minutes to cook. Fish is done when the skin is golden-brown and the flesh inside the cuts is white and opaque.
Turn off the heat and remove fish from oil. Set it on the paper towel to drain and crisp up. Meanwhile, place sauce over medium heat for a minute or two - just until warm enough to serve. Tip: Don't overheat. If you boil the sauce, you will lose its wonderfully fresh flavor!
To serve, place fish on a large plate or platter, and surround it with the sauce. Garnish with slices of tomato and/or cucumber, plus a few sprigs of coriander and basil. Note that the sauce is very strong, so you'll only need a little with each bite of fish. ENJOY!