0_7957 A recent experiment by the Cornell group suggests that a ground-state excitonic insulator, in which interlayer pairing of electron and holes develops, has been achieved using heterostructures of two-dimensional materials. In our recent proposal [arXiv:2210.03658] we show that polaron spectroscopy, a tool which has already been useful in probing other many-body states in two-dimensional materials (Wigner crystals, anomalous Hall effect, Mott states etc.), yields further insight on the nature of the excitonic insulator.In particular, we analyze a scheme where an optically generated intralayer exciton is screened by excitations out of the excitonic insulator to form interlayer polarons. Simulating 4-body systems with Quantum Monte-Carlo, we first determine the binding energy of the biexciton state composed of inter- and intralayer excitons, which plays a central role in understanding polaron formation.We describe the excitations out of the ground-state condensate using BCS theory and use a single interacting-quasiparticle-pair excitation Ansatz to describe dynamical screening of optical excitations. This technique allows to interpolate between the Bose regime at small interlayer distance and density, where the ground states excitons are tighly bound, and the BCS regime at large distance and density. In the BCS regime the oscillator strength transfer from the repulsive to the attractive polaron is enhanced. Also, a weaker peak appears in the regime where the trion binding energy and the pairing gap are comparable, and provides a direct estimate of the interlayer exciton binding energy. Exciton density and spontaneous spin-valley polarizationcan also be easily read off from the polaron spectra.In conclusion, the polaron spectra carry the hallmarks of the excitonic insulator phase.