  Hawking's quasi-local energy definition quantifies the energy enclosed by a
spacelike 2-sphere in terms of the amount of lightbending on the sphere caused
by the energy distribution inside the sphere. This paper establishes for the
first time a direct connection between the formal mathematical definition of a
quasi-local energy and observations, in the context of cosmological
perturbation theory. This is achieved by studying the Hawking Energy of
spherical sections of the past lightcone of a cosmic observer in a perturbed
Friedmann-Lema\^{i}tre spacetime. We express the Hawking Energy in terms of
gauge-invariant perturbation variables and comment on the cosmic observables
needed to in principle measure it. We then calculate its angular power spectrum
and interpret its contributions.
