To check your MLW climb gradient on one engine, have a look in FCOM OPS section under "Approach with Engine Failed". Its gives an OAT and pressure altitude maximum to achieve gradients from 2.5% through 7% (Only at max landing though).
I imagine your OPT (if you have one) will throw out the calculation if unable at the given weight (this may be company selectable option??). Options would be to raise the minima (HKG has a 2.5% grad. minima listed for example), or to fly the engine out departure profile (if there is one), or land elsewhere.
Hope this helps.