Clean the blue swimmers well. Remove and discard the spongy gills. Remove the top shell (carapace) and set aside and then cut the body into halves. If the claws are large, use a pestle to crack them.
Combine all the sauce base ingredients in a bowl and set aside.
Heat the oil in a large wok or deep pan. Add the garlic, chillies and shallots. Sauté in low to medium heat for a few minutes until fragrant.
Turn up the heat and add the crabs, inlcuding the top shells. Sauté until the shells turn red.
Lower the heat and add the sauce base and mix well with the crabs. Bring the sauce to a simmer, then taste and adjust the seasoning.
Mix the cornstarch with water to form a slurry, then pour it into the sauce so it thickens.
Crack the eggs into the thickened sauce. Using a fork or spatula, streak the eggs through the sauce vigorously until it is cooked through.
Remove the pan from the heat. If you want to, you can squeeze some lemon (to taste) over the sauce and mix it through.
Plate the crabs and sauce onto a large serving plate and place the top shell on the top. Garnish with coriander to serve.